Of a microphone, loudspeaker etc. Depending for its action on the movement of a coil in a magnetic field.
"I received CD's and MP3 CD's yesterday for the 3 reel-to-reel tapes I sent in. These were pretty old tapes (one around 33 years old) that had not been on a player since the 1980's when my reel-to-reel recorder was stolen and never replaced. One of them, in particular, contained unreplaceable studio performance tracks from a record album I had ..."